Rick Santorum entered Congress with modest means. But not long after he left in 2006, the former two-term senator reaped the rewards of his time on Capitol Hill, earning more than $1 million last year in cash and stock for advising corporate clients, sharing his insights with social organizations, and consulting for media outlets.

"He has been, essentially, a stealth lobbyist," said Bill Allison, editorial director for the Sunlight Foundation, a watchdog group. "He has been hired to try to influence policy on behalf of his clients without crossing the thresholds that would require him to report what he's doing."

The rural Pennsylvania politician who boasts his common man appeal has traveled a familiar path for those who have left public service, Allison said. After helping to shape policy on the Senate finance and banking committees, Santorum accepted paid consultant jobs for insurance and energy firms with key issues pending before the politician's former colleagues.

The work has been lucrative -- in 1996 he reported assets ranging from $155,000 to $475,000 on the personal financial disclosure form he filed with the Senate. The report he filed in August 2011 as he began his presidential bid show his assets are now valued between $1.9 million and $4 million, including rental properties and robust investment and college savings funds.

A spokesman for Santorum has not responded to calls and emails seeking comment.

Since leaving Congress Santorum has worked for at least seven different employers simultaneously, with several paying him a six-figure fee. As long as Santorum was not directly contacting members of Congress on behalf of his clients, he was not required to register as a federal lobbyist and disclose his activities. Only when he filed to run for president did he have to reveal these financial relationships.

He signed on with the American Continental Group, a lobbying firm co-founded by the late Peter Terpeluk, Jr., an ambassador and one-time finance chairman for the Republican National Committee. There he has reported helping insurance giant Fortegra Financial. Lobbying reports show the Florida-based insurance company hired the D.C. lobbying firm to help monitor the potential impact that Wall Street reform legislation would have on its business.

Allison said someone like Santorum would be extremely valuable in that regard. "He's an expert on the legislative process. He knows who the players are," Allison said. "Even if he's not contacting people, he can tell them where the levers are, who is receptive to hearing a message. And he also knows how the system works with money and influence, and can offer advice about who to contribute to, which leadership PACs to pump money."

Santorum also joined the board of Universal Health Services Inc. (UHS), a publicly traded health-care management firm that owns hospitals and healthcare facilities around the country. The company paid him nearly $400,000 in director fees and stock options before he stepped down from the board last year. The company has long served as a source of political support for Santorum, with company CEO Alan B. Miller serving as a major contributor to the senator and, now, presidential candidate.

Tony Pantaleoni, a fellow board member of Santorum's at UHS, said the politician's background in the Senate was a major asset to the company.

"There are always times that government involvement plays a role in our work," Pantaleoni told ABC News. "Knowing who the right people are to talk to, finding out what their concerns are, it was very helpful because he knew. He came with a wealth of knowledge about the various departments and issues. We were very glad with his service."

Justice Dept. Investigates UHS for Alleged Medicaid Fraud

While Santorum served on the board, UHS faced allegations from the U.S. Department of Justice that it engaged in Medicaid fraud. U.S. Attorney for the Western District of Virginia Timothy J. Heaphy alleged at the time that the company billed Medicaid for psychiatric medical care it never provided. "We will not sit idly by and allow healthcare providers to take advantage of troubled children in order to feed their own desire for wealth," he said. "The Medicaid system was designed to help the most vulnerable among us, not to line the pockets of fraudsters." Court records show the company disputed the charges and, earlier this year, the case entered settlement negotiations. UHS has not responded to calls from ABC News seeking comment on the case.

When asked about the Virginia case recently, Santorum told Yahoo News, "Any investigation, you obviously engage and fully cooperate with it, and that's what we did ... that's part of the responsibility of directors."

Miller, the UHS chairman, praised Santorum's work for the company, saying upon Santorum's departure from the board last year that "Rick's guidance and stewardship will be sorely missed."

Another of Santorum's post-Senate employers has been Consol Energy Inc., a Pennsylvania firm that describes itself as the leading diversified fuel producer in the eastern United States, responsible for mining more high-quality bituminous coal than any other U.S. producer.

Santorum also joined a Virginia-based consulting firm called the Clapham Group, which was founded in 2007 by Rick Rodgers, who served for 16 years as the former senator's chief of staff. A co-founder was media coordinator for the Senate Republican Conference under Santorum. The group's clients have ranged from the Jonas Brothers to the American Bible Society, according to the firm's web site. Clapham says its mission is to "influence culture upstream of the political arena." He received $125,000 for his efforts on behalf of the firm's clients.

At the same time, Santorum's experience and standing in national conservative circles helped him broker lucrative media contracts, including a $239,153-a-year consulting deal with Fox News and a talk radio contract with California-based Salem Radio.

By Washington standards, Allison said, Santorum has had a typical career trajectory -- not unlike that of many Democrats and Republicans, including Newt Gingrich, another former D.C. insider who has returned to politics to seek the GOP nomination for president in 2012.

"It's trading on your Washington expertise to make a good bit of money," Allison said. "It's a common practice."